A rotary distributor of this type is described in document FR 2 791 598 in the name of the Applicant. With reference to FIG. 1 of the attached drawings, the rotary distributor denoted in its entirety by the reference 1, comprises two coaxial rings 2, 3, theoretically with their axis A substantially vertical in the conditions of use as shown in FIG. 1. One of the rings (the ring 2 situated underneath in FIG. 1) is stationary, and the other ring (the ring 3 situated on top in FIG. 1) is rotary. The rings are in contact with one another in a sealed manner via respective facing contact faces 4, 5 defining a meeting plane P. The rotary ring 3 comprises communication orifices, denoted generically by the reference 6, which are each able to be connected to at least one individual treatment station for treating a container and which open into the contact face 5 of said rotary ring 3. The stationary ring 2 comprises at least one slot, denoted generically by the reference 7, which is able to be connected, at 8, to a pressure source of the machine and which opens into the contact face 4 of said stationary ring 2 in such a way as to lie in the path of the orifices 6 in the rotary ring 3; hence, a treatment station is placed in communication with the pressure source when the corresponding orifice 6 lies facing the slot 7.
In its design as described and depicted in document FR 2 791 598, the rotary distributor 1 is arranged with orifices 6 for connection to the treatment stations which are distributed over two circumferences, denoted generically by the reference 9, of different diameters (the orifices situated on these two, external 9e and internal 9i, circumferences being denoted 6e, 6i respectively) and with at least two slots 7e, 7i for connecting to at least one pressure source which, too, are situated on two circumferences, also denoted by the references 9e, 9i, of the same diameters as the diameters on which said orifices 6e, 6i are situated. This arrangement can be clearly seen from FIG. 2 of the attached drawings, which is a view of the rotary ring 3 from beneath, and in FIG. 3, which is a view of the stationary ring 2 from above. FIG. 3 shows that the slots 7 are distributed in several groups corresponding to the generation of several pressure levels: two slots 7e1, 7i1 are connected respectively to pumps involved in a first pumping step (pumping to a first vacuum level); two slots 7e2, 7i2 are connected respectively to pumps used in a second pumping step (pumping to a second, lower, vacuum level). In addition, two slots 15e, 15i are both connected, via a single common line 16, to a pump used for a vacuum using step (for example depositing a layer of a material such as carbon on a face—particularly the internal face—of a container made of thermoplastic such as PET, using a low-pressure plasma).
In this known arrangement, the radial distance between the two circumferences 9e and 9i is not very high (typically being of the order of magnitude of the diameter of an orifice 6, as can be seen in FIG. 2), whereas the internal circumference 9i is approximately 6 orifice 6 diameters away from the axis A of the rotary distributor.
This known arrangement is currently used in rotary machines that typically have 20 treatment stations, and is entirely satisfactory.
However, container manufacturers, particularly bottle manufacturers, are ever wishing to increase production rates. For certain treatments, (for example, for depositing a barrier layer, particularly of carbon, on the interior face of containers made of thermoplastics such as PET by using a low-pressure plasma), it is not possible to increase to any appreciable extent the rate at which the treatment process is performed at each station. A significant increase in the production rate can therefore be envisaged by increasing the number of treatment stations. Hence, the Applicant Company envisages developing a new machine in which the number of treatment stations is appreciably higher, and typically is more than doubled (to 48 stations).
In terms of the rotary distributor, that may result in a corresponding increase in the number of connections to be made, that is to say typically may correspond to at least doubling the number of communication orifices to be provided in the rotary ring.
However, rotary distributor rings are very large and heavy components; typically, in present-day machines equipped with 20 treatment stations, the rings are approximately 0.60 m in diameter and each weigh of the order of 120 kg. While it still remains possible to increase their outside diameter a little, the capability of the machines needed to manufacture these rings does, however, set a limit that cannot be crossed, even though it would be necessary to cross this limit in order to distribute the increased number of communication orifices over the same number (typically two) of circumferences of different diameters.
In order for the rings to maintain approximately their current diameter, it is therefore necessary to distribute the communication orifices over a larger number (typically 3 or even 4) of circumferences of different diameters. This objective can be achieved by reducing the diameter of the central aperture 10 of the rings 2, 3, and by populating the available surface area of the ring as densely as possible. By way of example, FIG. 4 shows from beneath a rotary ring 3 arranged in a configuration of this type with the orifices 6 distributed over three groups 6e, 6m, 6i situated respectively on three circumferences 9e, 9m, 9i, these respectively being the external, the middle and the internal ones.
However, in this case, as can be seen in FIG. 4, the diameter of the external circumference 9e is practically twice the diameter of the internal circumference 9i, and the internal circumference 9i is now only about 3 orifice 6 diameters away from the axis A. That means that the linear rate of travel of the orifices 6e situated on the external circumference 9e is practically twice that of the orifices 6i situated on the internal circumference 9i. As a result, if all the orifices 6 have the same shape—here a circle of the same diameter—as illustrated in FIG. 4, the rates at which the passages defined by an orifice 6 coinciding with an associated slot 7 open and close will differ according to the circumference: this rate will be higher for orifices 6e situated on the external circumference than for orifices 6i situated on the internal circumference 9i. This means that the treatment stations do not all receive the pressure in the same way and that, as a result, the containers are not all treated uniformly, according to the position of the control orifice on the rotary distributor.
Such inconsistency in the quality of container treatment is inadmissible.